1. Field of the Invention
The invention relates to a multiple stage hydraulic telescopic cylinder with at least two hollow pistons displaceable one within the other and annular spaces between the individual telescoping sliding members; with a pressure medium conduit connected to the pressure space of the cylinder; and a pressure medium conduit connected to the annular space of the cylinder; a connection between the pressure space of the cylinder and the pressure space of the intermediate piston, and a connecting passage between the inner space of the piston and a connecting passage on the circumference of the cylinder; in the bottom of the intermediate piston as well as connections between the annular space of the cylinder and the inner space of the intermediate piston on the one hand and the annular space of the intermediate piston and the inner space of the lifting piston on the other hand.
2. The Prior Art
For mechanical reasons it is often desirable that in the construction of such multistage telescoping cylinders the first stage should be completely moved out before the outward movement of the following stage begins. In the construction of such a telescoping cylinder it is further more desirable that in the reverse travel the entrance of the following stage should first begin when the preceding stage has moved in. For telescopic arrangements, which operate with such telescoping cylinders, the same is true.
To provide a separate cylinder for each outward stage is from an apparatus point of view expensive. Besides the pipe connections necessary for the expansion stages beyond the first stage are subject to damage. There has been proposed the use of multistage telescoping cylinders, in which attempts have been made to achieve the desired type of and manner of outward and inward movement among other things through a surface dependent control for the operation of the telescoping parts. However the disadvantage is present with the surface dependent control that the control during progressive outward movement of the telescoping cylinders and the arm is rendered inaccurate through the frictional force which exists in all cases between the telescopic slides. It is naturally possible also to provide a valve controlled regulation for such telescoping cylinders, but such a solution is on the contrary from the point of view of construction very expensive and because of the number of control elements very subject to disturbance.